This invention relates to top drive drilling equipment, and particularly to improved pipe handling apparatus for use therewith.
In a top drive drilling system, there is substituted for the usual rotary table, kelly, and related equipment an assembly which is connected to the upper end of the drill string and moves upwardly and downwardly therewith and has a motor driving a rotary element or stem connected to the string and acting to turn it. The powered top drive assembly is usually guided in its upward and downward movement by tracks or guide elements fixed to the rig derrick or mast.
One type of top drive drilling rig previously utilized includes pipe handling mechanism connected to the bottom of the powered top drive assembly and consisting of a torque wrench and elevator which are attached to the power driven rotary element of the top drive assembly and rotate with it while a well is being drilled. When the rotation of that element and the drill string is stopped, the torque wrench can be utilized to break a threaded connection between the powered rotary element of the top drive assembly and the drill string, and the elevator can be used to suspend a section of pipe during connection to or detachment from the remainder of the string.
This previously devised pipe handling equipment has had several operational disadvantages in use, a number of which have resulted in large part from the fact that the entire pipe handling assembly rotates with the drill string while drilling. For one thing, it must necessarily be extremely difficult in such an arrangement to balance the entire rotating pipe handling assembly with respect to its rotary axis in a manner avoiding the development of vibrational forces or movements as the assembly turns. Also, these rotating non-circular parts can be dangerous to personnel and other equipment, and inherently inconvenient for other reasons. In addition, the prior equipment being discussed is constructed in a manner requiring that the rotation of the torque wrench and elevator be halted in a predetermined rotary position for proper manipulation of the apparatus when the pipe handling equipment is being utilized near the rig floor for making and breaking a connection, and requiring that the wrench and elevator be turned to a different position for engaging and lifting pipe from a rack at an elevated location in the rig. It is frequently very difficult to halt the rotation of a powered top drive assembly at precisely a predetermined rotary position, and thus substantial time and effort can be lost if such controlled rotary positioning is critical. Another disadvantage of the prior equipment resides in the fact that the torque wrench portion of such apparatus is inherently incapable of breaking a threaded connection between the top drive unit and the drill string at an elevated location in the rig since the hydraulic or other connections to the torque wrench which are required for actuating and controlling it must be broken while the torque wrench is rotating with the drill string, and can not conveniently be reconnected near the top of the rig.